There are known methods of producing metallic titanium by the reduction of titanium tetrachloride using magnesium or sodium with the subsequent crushing and melting of spongy titanium in a vacuum-arc furnace to obtain ingots. These are variations of Kroll's method. With any version of the technological process of metallothermic reduction using Kroll's method, a purified titanium tetrachloride is fed into a sealed reactor that is filled with argon. A reducing agent is already present in the reactor or is fed into the reactor simultaneously with the titanium tetrachloride. The upper limit of the temperature of the process is limited by the durability of the steel equipment used, and the lower limit is determined by the melting point of the chlorides obtained as a result of reduction. After the completion of the titanium tetrachloride reduction by the reducing agent and the vacuum separation of the products of the reaction (usually in a magnesium-thermic process), a titanium sponge is extracted from the reactor by drilling or by pressing out. Then the titanium sponge is crushed. Then the crushed titanium sponge is melted down to ingots. This method is described in “Titanium. Properties, Source Of Raw Materials, Physicochemical Fundamentals And Method Of Obtaining Thereof,” (Moscow) Metallurgy, 1983, p. 339-342 (, ,  , -    . M.: , 1983. C. 339-342)
Traditionally, the melting of titanium sponge has been conducted either in a vacuum-arc furnace or in an atmosphere of inert gas. However, melting in a vacuum has the advantage that during the melting the bath of metal boils. The removal of volatile impurities, such as hydrogen, moisture, reducing agent and reducing agent chloride) from metallic titanium is conducted considerably faster than during the melting under the pressure of an inert gas. Melting in a vacuum produces a better quality metal. One known technological scheme for producing metallic ingots of titanium by melting in a vacuum-arc furnace involves a primary melting of a consumable electrode that is made of the pressed titanium sponge. An electric arc burns between a bath of liquid metal and the consumable electrode, and the melting metal flows down to the bath. A secondary melting is conducted in a casting mold of larger diameter than that used in the primary melting. The consumable electrodes for the secondary melting are produced by welding together several electrodes obtained from the primary melting. This method is described in “Titanium Metallurgy,” (Moscow) Metallurgy, 1964, p. 182-184 ( . M.: , 1964. C. 182-184).
The main disadvantage of these methods is that the process of producing metallic titanium is divided into several stages. This leads to a long duration of the process of producing metallic titanium and to low productivity of the devices that implement these methods.
Another method of producing metallic titanium involves reducing titanium from its chloride using a reducing metal and a reducing agent. U.S. Pat. No. 3,847,596, entitled “Process of obtaining metals from metal halides”, describes feeding a titanium chloride (such as titanium tetrachloride in a gaseous form) and a reducing agent (such as liquid magnesium) into an evacuated and pre-heated reactor in which an exothermic reaction occurs. The reduction reaction is achieved at a temperature higher than the melting point of the metal to be produced and at a pressure not lower than the pressure of evaporating gases of the reducing agent chloride. First, titanium is formed in a solid form. As a result of the reduction reaction, the reducing agent chloride is heated under atmospheric pressure to a vaporization temperature and changes to a gaseous state until the pressure of the gases (pressure of molten reducing agent chloride, pressure of molten titanium and pressure of inert gas introduced into the reactor) reaches the pressure that corresponds to the temperature of substitution in the reaction. From this point on, the reducing agent chloride appears only in a liquid state. The subsequent substitution occurs at the pressure of the obtained flux and at a temperature higher than the melting point of titanium. The result of the process is melted titanium. Thus liquid titanium is produced in the reactor. The chloride of the liquid reducing agent forms a layer and floats on the surface of the liquid titanium. The liquid titanium is continuously removed from the reactor through a cooled copper ingot mold under an argon atmosphere or in a vacuum.
A disadvantage of this method is that the metallic titanium obtained is heavily saturated with residual chlorine, metallic magnesium and magnesium chloride, as well as with hydrogen and other gases that are generated from the admixtures of titanium tetrachloride and reducing agent. Furthermore, the industrial application of this method is complicated by the problem of obtaining a material for the reactor that can withstand temperatures higher than the melting point of titanium.
Yet another known method of producing metallic titanium enables the continuous production of metallic titanium through the reduction of titanium tetrachloride by a reducing agent. This method is described in European Patent No. EP 0 299 791, entitled “Method for producing metallic titanium and apparatus therefor.” The method requires the temperature in a reaction zone of a reactor to exceed the melting point of titanium. The pressure in the reaction zone must exceed the pressure of a gaseous reducing agent. The method involves supplying titanium tetrachloride and the reducing agent (e.g., magnesium) into the reactor such that metallic titanium and by-product (the chloride of the reducing agent) are produced while the metallic titanium and by-product are maintained in a molten form. The metallic titanium and the by-product are separated by using the difference in their densities. Metallic titanium is collected at and continuously extracted from the bottom of the reactor.
The device used for this method includes the reactor, pipes for supplying titanium tetrachloride and the reducing agent, heating elements and means for extracting the metallic titanium. The reactor has a reaction zone for maintaining a temperature higher than the melting point of titanium and for maintaining a pressure sufficient to prevent the boiling of the reducing agent (e.g., magnesium) and its chloride. There is one pipe for supplying the reducing agent in a liquid state into the reaction zone through the reactor's lateral side or upper part. There is another pipe for supplying titanium tetrachloride into the reaction zone through the reactor's upper part. The by-product (the chloride of the reducing agent) is discharged through a discharge pipe from the reactor's lateral side. Heating elements are mounted on the reactor's outer side at the level of the reaction zone. The device has a means for continuously extracting metallic titanium from the bottom of the reactor.
A disadvantage of this method is the need to maintain a high pressure (about 50 atmospheres) in the reaction zone in order to prevent the reducing agent and its chloride from boiling. In addition, a temperature must be maintained in the reaction zone that exceeds the melting point of titanium. The high temperature and pressure requirements of this method create problems from escaping gas and even bursting reactors. Thus, this method provides an insufficient level of safety for producing metallic titanium. Furthermore, producing metallic titanium at high pressure in the rector leads to a heavy saturation of the metallic titanium by chlorine residue, metallic magnesium, magnesium chloride, hydrogen and other gases generated from titanium tetrachloride admixtures and the reducing agent. The heavy saturation with impurities leads to producing metallic titanium of insufficient quality.